. >> president obama and mitt romney facing off in the first of three debates. abc's karen travers is in denver with a preview. >> reporter: with president obama and mitt romney doing final debate preps, their runningmates hit the campaign trail. vice president biden was speaking about romney's economic plans when he said this -- >> how they can justify raising taxes on the middle-class that has been buried the last four years. >> reporter: republicans called it a stunning admission that the middle-class has been hurt by the obama administration's policies. congressman paul ryan pounced. >> of course the middle-class has been buried, buried by regulations, buried by taxes, buried by borrowing, they're being buried by the obama administration's economic failures. >> biden later tried to dig himself out. >> the middle class was buried by the policies of romney and the ryan supported. >> reporter: except for debate prep, a politics-free day for contenders. romney had lunch at chipotle. president obama paid a visit to the hoover dam. both have spent hours in debate